[PATCH 4.19 34/36] irqchip/gic: Atomically update affinity

Greg Kroah-Hartman
2020-07-07T15:19:23Z

From: Marc Zyngier <maz@kernel.org>

commit 005c34ae4b44f085120d7f371121ec7ded677761 upstream.

The GIC driver uses a RMW sequence to update the affinity, and
relies on the gic_lock_irqsave/gic_unlock_irqrestore sequences
to update it atomically.

But these sequences only expand into anything meaningful if
the BL_SWITCHER option is selected, which almost never happens.

It also turns out that using a RMW and locks is just as silly,
as the GIC distributor supports byte accesses for the GICD_TARGETRn
registers, which when used make the update atomic by definition.

Drop the terminally broken code and replace it by a byte write.

Fixes: 04c8b0f82c7d ("irqchip/gic: Make locking a BL_SWITCHER only feature")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/irqchip/irq-gic.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)

--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -324,10 +324,8 @@ static int gic_irq_set_vcpu_affinity(str
static int gic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
bool force)
{
- void __iomem *reg = gic_dist_base(d) + GIC_DIST_TARGET + (gic_irq(d) & ~3);
- unsigned int cpu, shift = (gic_irq(d) % 4) * 8;
- u32 val, mask, bit;
- unsigned long flags;
+ void __iomem *reg = gic_dist_base(d) + GIC_DIST_TARGET + gic_irq(d);
+ unsigned int cpu;

if (!force)
cpu = cpumask_any_and(mask_val, cpu_online_mask);
@@ -337,13 +335,7 @@ static int gic_set_affinity(struct irq_d
if (cpu >= NR_GIC_CPU_IF || cpu >= nr_cpu_ids)
return -EINVAL;

- gic_lock_irqsave(flags);
- mask = 0xff << shift;
- bit = gic_cpu_map[cpu] << shift;
- val = readl_relaxed(reg) & ~mask;
- writel_relaxed(val | bit, reg);
- gic_unlock_irqrestore(flags);
-
+ writeb_relaxed(gic_cpu_map[cpu], reg);
irq_data_update_effective_affinity(d, cpumask_of(cpu));

return IRQ_SET_MASK_OK_DONE;